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import { not } from '../util/not';
import { filter } from './filter';
import { Observable } from '../Observable';
import { UnaryFunction } from '../types';
/**
* Splits the source Observable into two, one with values that satisfy a
* predicate, and another with values that don't satisfy the predicate.
*
* <span class="informal">It's like {@link filter}, but returns two Observables:
* one like the output of {@link filter}, and the other with values that did not
* pass the condition.</span>
*
* 
*
* `partition` outputs an array with two Observables that partition the values
* from the source Observable through the given `predicate` function. The first
* Observable in that array emits source values for which the predicate argument
* returns true. The second Observable emits source values for which the
* predicate returns false. The first behaves like {@link filter} and the second
* behaves like {@link filter} with the predicate negated.
*
* ## Example
* Partition click events into those on DIV elements and those elsewhere
* ```javascript
* import { fromEvent } from 'rxjs';
* import { partition } from 'rxjs/operators';
*
* const clicks = fromEvent(document, 'click');
* const parts = clicks.pipe(partition(ev => ev.target.tagName === 'DIV'));
* const clicksOnDivs = parts[0];
* const clicksElsewhere = parts[1];
* clicksOnDivs.subscribe(x => console.log('DIV clicked: ', x));
* clicksElsewhere.subscribe(x => console.log('Other clicked: ', x));
* ```
*
* @see {@link filter}
*
* @param {function(value: T, index: number): boolean} predicate A function that
* evaluates each value emitted by the source Observable. If it returns `true`,
* the value is emitted on the first Observable in the returned array, if
* `false` the value is emitted on the second Observable in the array. The
* `index` parameter is the number `i` for the i-th source emission that has
* happened since the subscription, starting from the number `0`.
* @param {any} [thisArg] An optional argument to determine the value of `this`
* in the `predicate` function.
* @return {[Observable<T>, Observable<T>]} An array with two Observables: one
* with values that passed the predicate, and another with values that did not
* pass the predicate.
* @method partition
* @owner Observable
*/
export function partition<T>(predicate: (value: T, index: number) => boolean,
thisArg?: any): UnaryFunction<Observable<T>, [Observable<T>, Observable<T>]> {
return (source: Observable<T>) => [
filter(predicate, thisArg)(source),
filter(not(predicate, thisArg) as any)(source)
] as [Observable<T>, Observable<T>];
}
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